A diffusion heat treatment method for a cerium-containing neodymium-iron-boron magnet

Abstract

The application discloses a diffusion heat treatment method suitable for a cerium-containing neodymium-iron-boron magnet, relates to the technical field of rare earth permanent magnet materials, and specifically comprises the following steps: S10: applying a diffusion source of heavy rare earth elements on the surface of the magnet; S20: performing heat treatment on the magnet coated with the diffusion source under vacuum conditions, including: S21: performing degassing and degreasing treatment on the magnet by heating the magnet from room temperature to 250-550 DEG C; S22: after the magnet is heated from 550 DEG C to 750 DEG C, the magnet is heated from 750 DEG C to 850 DEG C at a rate of 0.05-0.1 DEG C / min; S23: the magnet is heated from 850 DEG C to 930-970 DEG C, and after being kept warm for 0.5-5 hours, the magnet is cooled to room temperature; and S24: the magnet is heated from room temperature to 600-680 DEG C under vacuum conditions, and after heat treatment for 0.5-6 hours, the magnet is cooled to room temperature; and the application can significantly improve the coercive force of the cerium-containing neodymium-iron-boron magnet.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, specifically to a diffusion heat treatment method suitable for cerium-containing neodymium iron boron magnets. Background Technology

[0002] To achieve high-value utilization of cerium-containing NdFeB permanent magnet materials, grain boundary diffusion technology is typically used to introduce heavy rare earth elements such as Dy and Tb from the magnet surface into the interior to improve coercivity. However, in existing heavy rare earth diffusion processes, when held at the same temperature range, rare earth elements easily undergo elemental substitution with the CeFe2 phase, forming a large amount of (Ce,HRE)Fe2 ineffective phase, resulting in reduced utilization of heavy rare earth elements and limited improvement in coercivity. Summary of the Invention

[0003] The purpose of this invention is to provide a diffusion heat treatment method suitable for cerium-containing NdFeB magnets, which can reduce the formation of (Ce, HRE)Fe2 phase and significantly improve the coercivity of cerium-containing NdFeB magnets.

[0004] To achieve the above objectives, the solution of the present invention is as follows:

[0005] A diffusion heat treatment method suitable for cerium-containing NdFeB magnets includes the following steps:

[0006] S10: A diffusion source for coating heavy rare earth elements on the surface of a magnet;

[0007] S20: The magnet coated with the diffusion source is heated under vacuum conditions. The heating process includes:

[0008] S21: Degas and degrease the magnet by heating it from room temperature to 250-550℃;

[0009] S22: After heating the magnet from 550℃ to 750℃, and then heating it from 750℃ to 850℃ at a rate of 0.05-0.1℃ / min, the temperature at which the CeFe2 phase melts into a liquid phase in the magnet is 920℃.

[0010] S23: Heat the magnet from 850℃ to 930-970℃, which is higher than the temperature at which the CeFe2 phase melts into a liquid phase in the magnet, hold the temperature for 0.5-5 hours, and then cool it to room temperature.

[0011] S24: Heating from room temperature to 600-680℃ under vacuum conditions, heat-treated for 0.5-6 hours, and then cooled to room temperature.

[0012] Furthermore, in step S21, the temperature is maintained at 250℃, 350℃, and 550℃ for 30 minutes each.

[0013] Furthermore, the heating rates from room temperature to 250°C, from 250°C to 350°C, and from 350°C to 550°C are 5-10°C / min.

[0014] Furthermore, the magnet was heated from 750°C to 850°C at a heating rate of 0.1°C / min.

[0015] Furthermore, in step S22, the magnet is heated from 550°C to 750°C at a heating rate of 3-5°C / min.

[0016] Furthermore, in step S23, the magnet is heated from 850°C to within 930-970°C at a heating rate of 5-8°C / min, and then cooled to room temperature at a rate of 15-20°C / min.

[0017] Furthermore, when cooling from 930-970℃ to room temperature, the cooling medium is argon gas at a pressure of 0.88 times the atmospheric pressure.

[0018] Furthermore, in step S24, the heating rate from room temperature to 600-680℃ is 5-8℃ / min, and the cooling rate from 600-680℃ to room temperature is 15-20℃ / min.

[0019] Specifically, the diffusion sources include one or more of rare earth element hydrides, rare earth element fluorides, and rare earth alloys. The rare earth elements include one or more of La, Ce, Pr, Nd, Ho, Dy, Tb, and Gd. The non-rare earth elements in the rare earth alloys include one or more of Al, Cu, Ga, Sn, and Zn.

[0020] Specifically, the diffusion source can be applied to NdFeB magnets by at least one of the following methods: spraying, printing, magnetron sputtering, static evaporation, spin evaporation, and electrophoretic deposition.

[0021] After adopting the above solution, the beneficial effects of the present invention are as follows:

[0022] This invention utilizes a slow, low-temperature heating process (0.05-0.1℃ / min) in step S22 to allow heavy rare earth elements to preferentially and steadily diffuse into the magnet along grain boundaries at temperatures below the melting point of the CeFe2 phase within the magnet. This process effectively reduces unnecessary elemental substitutions between heavy rare earth elements and the CeFe2 phase in the magnet, thereby significantly suppressing the formation of the (Ce, HRE)Fe2 ineffective phase. This allows more heavy rare earth elements to be used to strengthen the main phase grains, improving the utilization efficiency of expensive heavy rare earth elements and achieving cost reduction and efficiency improvement. Furthermore, the high-temperature, short-time heat treatment in step S23 melts the grain boundary phase (including the CeFe2 phase) while simultaneously creating conditions for heavy rare earth elements to diffuse to the surface of the main phase grains to form an HRE-rich shell. This is because heavy rare earth atoms (Dy, Tb reaches the main phase grain boundary through the liquid phase grain boundary channel, which can effectively pin magnetic domains and suppress the nucleation of antimagnetic domains, thereby significantly improving coercivity. More importantly, the 0.5-5 hour heat preservation limits the time window for continuous harmful reactions between heavy rare earth elements and CeFe2 phase at high temperature, making the improvement in coercivity much higher than that of traditional single temperature range diffusion processes. Attached Figure Description

[0023] Figure 1 This is a flowchart of the steps of the present invention;

[0024] Figure 2 This is a schematic diagram of temperature changes in the process steps of this invention. Detailed Implementation

[0025] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0026] like Figures 1 to 2 As shown, this embodiment provides a diffusion heat treatment method suitable for cerium-containing NdFeB magnets, including the following steps:

[0027] S10: A diffusion source for coating heavy rare earth elements on the surface of a magnet;

[0028] S20: The magnet coated with the diffusion source is heated under vacuum conditions. The heating process includes:

[0029] S21: Degas and degrease the magnet by heating it from room temperature to 250-550℃;

[0030] S22: After heating the magnet from 550℃ to 750℃, and then heating it from 750℃ to 850℃ at a rate of 0.05-0.1℃ / min, the temperature at which the CeFe2 phase melts into a liquid phase in the magnet is 920℃.

[0031] S23: Heat the magnet from 850℃ to 930-970℃, which is higher than the temperature at which the CeFe2 phase melts into a liquid phase in the magnet, hold the temperature for 0.5-5 hours, and then cool it to room temperature.

[0032] S24: Heating from room temperature to 600-680℃ under vacuum conditions, heat-treated for 0.5-6 hours, and then cooled to room temperature.

[0033] Furthermore, in step S21, the temperature is maintained at 250℃, 350℃, and 550℃ for 30 minutes each.

[0034] Furthermore, the heating rate from room temperature to 250℃, from 250℃ to 350℃, and from 350℃ to 550℃ is 5-10℃ / min.

[0035] Preferably, the magnet is heated from 750°C to 850°C at a heating rate of 0.1°C / min.

[0036] Furthermore, in step S22, the magnet is heated from 550°C to 750°C at a heating rate of 3-5°C / min.

[0037] Furthermore, in step S23, the magnet is heated from 850°C to within 930-970°C at a heating rate of 5-8°C / min, and then cooled to room temperature at a rate of 15-20°C / min.

[0038] Specifically, when cooling from 930-970℃ to room temperature, the cooling medium is argon gas at a pressure of 0.88 times the atmospheric pressure.

[0039] Furthermore, in step S24, the heating rate from room temperature to 600-680℃ is 5-8℃ / min, and the cooling rate from 600-680℃ to room temperature is 15-20℃ / min.

[0040] Furthermore, the diffusion source includes one or more of rare earth element hydrides, rare earth element fluorides, and rare earth alloys. The rare earth elements include one or more of La, Ce, Pr, Nd, Ho, Dy, Tb, and Gd. The non-rare earth elements in the rare earth alloys include one or more of Al, Cu, Ga, Sn, and Zn.

[0041] Furthermore, the diffusion source can be applied to the NdFeB magnet by at least one of spraying, printing, magnetron sputtering, static evaporation, spin evaporation, and electrophoretic deposition.

[0042] Specifically, the first stage of heat preservation (250℃) mainly removes physically adsorbed water and some crystal water. The magnet and coating will adsorb moisture in the air. The heat preservation at 250℃ causes this moisture to evaporate and be extracted by the vacuum pump.

[0043] The second stage of heat preservation (350℃) is the core of which is to decompose and remove organic adhesives. If the diffusion source is applied by spraying, printing or other methods, organic solvents or polymers are usually used as adhesives. The 350℃ heat preservation allows these organic substances to decompose and carbonize slowly and evenly, volatilizing gases such as hydrocarbons, thus avoiding rapid boiling at high temperatures that could cause the coating to blister and peel off.

[0044] The third stage involves heat preservation (550℃). If the diffusion source is dysprosium hydride (DyH3) ​​or terbium hydride (TbH3 / TbH2), they begin to decompose and release hydrogen (H2) near this temperature, leaving behind highly active heavy rare earth metal atoms to prepare for subsequent diffusion. This process needs to be carried out smoothly to avoid the instantaneous release of large amounts of hydrogen.

[0045] The present invention provides the following embodiments and comparative examples, through which the improvement in coercivity of neodymium iron boron magnets after the technical solution of the present invention is demonstrated:

[0046] Example 1:

[0047] This embodiment provides a grain boundary diffusion heat treatment method for a 6 wt.% cerium-containing substrate, including the following steps:

[0048] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0049] (2) Place the 6 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0050] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0051] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0052] (5) Set the heating rate to 0.1℃ / min and heat from 750℃ to 850℃;

[0053] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0054] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0055] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0056] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0057] Example 2:

[0058] This embodiment provides a grain boundary diffusion heat treatment method for a 9wt.% cerium-containing substrate, including the following steps:

[0059] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0060] (2) Place the 9wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10. -3 Pa;

[0061] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0062] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0063] (5) Set the heating rate to 0.1℃ / min and heat from 750℃ to 850℃;

[0064] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0065] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0066] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0067] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0068] Example 3:

[0069] This embodiment provides a grain boundary diffusion heat treatment method for a 12wt.% cerium-containing substrate, including the following steps:

[0070] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0071] (2) Place the 12 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0072] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0073] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0074] (5) Set the heating rate to 0.1℃ / min and heat from 750℃ to 850℃;

[0075] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0076] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0077] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0078] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0079] Comparative Example 1:

[0080] This comparative example provides a grain boundary diffusion heat treatment method for a 6 wt.% cerium-containing substrate, comprising the following steps:

[0081] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0082] (2) Place the 6 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0083] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0084] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0085] (5) Keep warm at 750℃ for 15 hours;

[0086] (6) Set the heating rate to 5℃ / min, and heat from 750℃ to 930℃ and hold for 2 hours;

[0087] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0088] (8) Evacuate to 1x10 -3Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0089] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0090] Comparative Example 2:

[0091] Comparative Example 2 provides a grain boundary diffusion heat treatment method for a 9 wt.% cerium-containing substrate, comprising the following steps:

[0092] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0093] (2) Place the 9 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0094] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0095] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0096] (5) Keep warm at 750℃ for 15 hours;

[0097] (6) Set the heating rate to 5℃ / min, and heat from 750℃ to 930℃ and hold for 2 hours;

[0098] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0099] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0100] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0101] Comparative Example 3:

[0102] This comparative example provides a grain boundary diffusion heat treatment method for a 12 wt.% cerium-containing substrate, comprising the following steps:

[0103] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0104] (2) Place the 12 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0105] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0106] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0107] (5) Keep warm at 750℃ for 15 hours;

[0108] (6) Set the heating rate to 5℃ / min, and heat from 750℃ to 930℃ and hold for 2 hours;

[0109] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0110] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0111] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0112] Table 1: Comparison of coercivity after diffusion between Examples 1-3 and Comparative Examples 1-3

[0113]

[0114] Example 4:

[0115] This embodiment provides a grain boundary diffusion heat treatment method for a 6 wt.% cerium-containing substrate, including the following steps:

[0116] (1) The preferred diffusion source is dysprosium hydride; the preferred coating method is spraying.

[0117] (2) Place the 6 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0118] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0119] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0120] (5) Set the heating rate to 0.1℃ / min and heat from 750℃ to 850℃;

[0121] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0122] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0123] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0124] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0125] Example 5:

[0126] This embodiment provides a grain boundary diffusion heat treatment method for a 9 wt.% cerium-containing substrate, including the following steps:

[0127] (1) The preferred diffusion source is dysprosium hydride; the preferred coating method is spraying.

[0128] (2) Place the 9 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0129] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0130] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0131] (5) Set the heating rate to 0.1℃ / min and heat from 750℃ to 850℃;

[0132] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0133] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0134] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0135] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0136] Example 6:

[0137] This embodiment provides a grain boundary diffusion heat treatment method for a 12 wt.% cerium-containing substrate, including the following steps:

[0138] (1) The preferred diffusion source is dysprosium hydride; the preferred coating method is spraying.

[0139] (2) Place the 12 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0140] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0141] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0142] (5) Set the heating rate to 0.1℃ / min and heat from 750℃ to 850℃;

[0143] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0144] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0145] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0146] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0147] Comparative Example 4:

[0148] This comparative example provides a grain boundary diffusion heat treatment method for a 6 wt.% cerium-containing substrate, comprising the following steps:

[0149] (1) The preferred diffusion source is dysprosium hydride; the preferred coating method is spraying.

[0150] (2) Place the 6 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0151] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0152] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0153] (5) Set the heating rate to 5℃ / min and heat from 750℃ to 850℃;

[0154] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0155] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0156] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0157] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0158] Comparative Example 5:

[0159] This comparative example provides a grain boundary diffusion heat treatment method for a 9 wt.% cerium-containing substrate, comprising the following steps:

[0160] (1) The preferred diffusion source is dysprosium hydride; the preferred coating method is spraying.

[0161] (2) Place the 9 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0162] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0163] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0164] (5) Set the heating rate to 5℃ / min and heat from 750℃ to 850℃;

[0165] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0166] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0167] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0168] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0169] Comparative Example 6:

[0170] This comparative example provides a grain boundary diffusion heat treatment method for a 12 wt.% cerium-containing substrate, comprising the following steps:

[0171] (1) The preferred diffusion source is dysprosium hydride; the preferred coating method is spraying.

[0172] (2) Place the 12 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0173] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0174] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0175] (5) Set the heating rate to 5℃ / min and heat from 750℃ to 850℃;

[0176] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0177] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0178] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0179] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0180] Table 2: Comparison of coercivity after diffusion between Examples 4-6 and Comparison 4-6

[0181]

[0182] Example 7:

[0183] This embodiment provides a grain boundary diffusion heat treatment method for a 9wt.% cerium-containing substrate, including the following steps:

[0184] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0185] (2) Place the 9 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0186] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0187] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0188] (5) Set the heating rate to 0.05℃ / min and heat from 750℃ to 850℃;

[0189] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0190] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0191] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0192] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0193] Comparative Example 7:

[0194] This embodiment provides a grain boundary diffusion heat treatment method for a 9wt.% cerium-containing substrate, including the following steps:

[0195] (1) Terbium hydride is preferably used as the diffusion source; spraying is preferably used as the coating method;

[0196] (2) Place the 9 wt.% cerium-containing substrate into a vacuum sintering furnace, close the furnace door, and evacuate to 1x10⁻¹. -3 Pa;

[0197] (3) Set the heating rate to 10℃ / min and keep warm at 250℃, 350℃ and 550℃ for 30min respectively;

[0198] (4) Set the heating rate to 3~5℃ / min and heat from 550℃ to 750℃;

[0199] (5) Set the heating rate to 0.01℃ / min and heat from 750℃ to 850℃;

[0200] (6) Set the heating rate to 5℃ / min, and heat from 850℃ to 930℃ and hold for 2 hours;

[0201] (7) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min;

[0202] (8) Evacuate to 1x10 -3 Pa, set the heating rate to 8℃ / min, and hold at 630℃ for 4 hours;

[0203] (9) Stop evacuating, fill with argon gas at 0.88 times atmospheric pressure, and cool; the cooling rate is 20℃ / min.

[0204] Table 3: Comparison of coercivity after diffusion between Example 7 and Comparative Example 7

[0205]

[0206] A comparison of Examples 1-3 and Comparative Examples 1-3 revealed that, with the same cerium content, the slow heating process at 0.1℃ / min was more effective in improving coercivity than the process of holding at 750℃ for 15 hours. This indicates that the slow heating process allows heavy rare earth elements to diffuse more preferentially and fully into the grain boundaries, rather than reacting with the CeFe2 phase, thereby significantly improving utilization.

[0207] A comparison of Examples 4-6 and Comparative Examples 4-6 revealed that, with the same cerium content, and different heating rates from 750°C to 850°C, a slow heating rate of 0.1°C / min was more effective in improving coercivity than a rapid heating rate of 5°C / min. This indicates that a slow heating rate of 0.1°C / min allows heavy rare earth elements to diffuse more preferentially and fully into the grain boundaries, rather than reacting with the CeFe2 phase, thus significantly improving utilization.

[0208] A comparison of Example 7 and Comparative Example 7 revealed that, with the same cerium content, the slow heating process at 0.05℃ / min was more effective in improving coercivity than the slow heating process at 0.01℃ / min. Furthermore, compared to Comparative Example 2, Example 7 showed that the slow heating process at 0.05℃ / min was more effective in improving coercivity than the process of holding at 750℃ for 15 hours.

[0209] Therefore, it can be concluded that, under the same cerium content, slowly heating from 750℃ to 850℃ at a heating rate of 0.05℃ / min-0.1℃ / min can more effectively improve the coercivity of cerium-containing NdFeB magnets, allowing heavy rare earth elements to diffuse more preferentially and fully into the grain boundaries rather than reacting with the CeFe2 phase, thereby significantly improving utilization.

[0210] The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. All equivalent changes made based on the key design features of this case shall fall within the protection scope of this case.

Claims

1. A diffusion heat treatment method suitable for cerium-containing neodymium iron boron magnets, characterized in that: Includes the following steps: S10: A diffusion source for heavy rare earth elements coated on the surface of the magnet; S20: The magnet coated with the diffusion source is heated under vacuum conditions. The heating process includes: S21: Degas and degrease the magnet by heating it from room temperature to 250-550℃; S22: After heating the magnet from 550℃ to 750℃, and then heating it from 750℃ to 850℃ at a rate of 0.05-0.1℃ / min, the temperature at which the CeFe2 phase melts into a liquid phase in the magnet is 920℃. S23: Heat the magnet from 850℃ to 930-970℃, which is higher than the temperature at which the CeFe2 phase melts into a liquid phase in the magnet, hold the temperature for 0.5-5 hours, and then cool it to room temperature. S24: Heating from room temperature to 600-680℃ under vacuum conditions, heat-treated for 0.5-6 hours, and then cooling to room temperature.

2. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: In step S21, the temperature is maintained at 250℃, 350℃ and 550℃ for 30 minutes each.

3. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 2, characterized in that: The heating rate is 5-10℃ / min for heating from room temperature to 250℃, from 250℃ to 350℃, and from 350℃ to 550℃.

4. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: The magnet was heated from 750°C to 850°C at a heating rate of 0.1°C / min.

5. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: In step S22, the magnet is heated from 550°C to 750°C at a heating rate of 3-5°C / min.

6. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: In step S23, the magnet is heated from 850°C to within 930-970°C at a heating rate of 5-8°C / min, and then cooled to room temperature at a rate of 15-20°C / min.

7. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: When cooling from 930-970℃ to room temperature, the cooling medium is argon gas at a pressure of 0.88 times the atmospheric pressure.

8. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: In step S24, the heating rate from room temperature to 600-680℃ is 5-8℃ / min, and the cooling rate from 600-680℃ to room temperature is 15-20℃ / min.

9. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: The diffusion sources include one or more of rare earth element hydrides, rare earth element fluorides, and rare earth alloys. The rare earth elements include one or more of La, Ce, Pr, Nd, Ho, Dy, Tb, and Gd. The non-rare earth elements in the rare earth alloys include one or more of Al, Cu, Ga, Sn, and Zn.

10. The diffusion heat treatment method for cerium-containing NdFeB magnets as described in claim 1, characterized in that: The diffusion source can be applied to NdFeB magnets by at least one of the following methods: spraying, printing, magnetron sputtering, static evaporation, spin evaporation, and electrophoretic deposition.

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